Prospectus: Risk/Return: Legal Entity Identifier Entity Inv Company Type Document Type Document Period End Date Registrant Name Entity Central Index Key Amendment Flag Amendment Description Trading Symbol Document Creation Date Document Effective Date Prospectus Date Performance Measure [Axis] Share Class [Axis] Document [Axis] Prospectus Coregistrant [Axis] Coregistrant [Domain] Series [Axis] Series S000065837 [Member] FlexShares US Quality Low Volatility Index Fund FlexShares US Quality Low Volatility Index Fund Member After Taxes on Distributions After Taxes on Distributions After Taxes on Distributions and Sale of Shares After Taxes on Distributions and Sales Before Taxes fst:Russell1000IndexMember Russell1000 Index [Member] Russell 1000® Index Northern Trust Quality Low Volatility Index Northern Trust Quality Low Volatility Index [Member] Northern Trust Quality Low Volatility Index℠ Share Classes C000212719 [Member] FlexShares US Quality Low Volatility Index Fund FlexShares US Quality Low Volatility Index Fund Risk [Axis] All Risks [Member] Risk Nondiversified Status [Member] Risk Lose Money [Member] Risk Money Market Fund Price Fluctuates [Member] Risk Money Market Fund May Impose Fees or Suspend Sales [Member] Risk Money Market Fund May Not Preserve Dollar [Member] Risk Money Market Fund Sponsor May Not Provide Support [Member] Risk Not Insured Depository Institution [Member] Risk Not Insured [Member] Equity Securities Risk Equity Securities Risk [Member] Low Volatility Risk Low Volatility Risk [Member] Quality Factor Risk Quality Factor Risk [Member] Concentration Risk Concentration Risk [Member] Market Risk Market Risk [Member] Index Risk Index Risk [Member] Tracking Error Risk Tracking Error Risk [Member] Sampling Risk Sampling Risk [Member] Authorized Participant Concentration Risk Authorized Participant Concentration Risk [Member] Calculation Methodology Risk Calculation Methodology Risk [Member] Market Trading Risk Market Trading Risk [Member] Derivatives Risks Derivatives Risks [Member] Mid Cap Stock Risk Mid Cap Stock Risk [Member] Securities Lending Risk Securities Lending Risk [Member] Management Fees Management Fees (as a percentage of Assets) Distribution (12b-1) Fees Distribution and Service (12b-1) Fees Other Expenses Other Expenses (as a percentage of Assets): Total Annual Fund Operating Expenses Expenses (as a percentage of Assets) Expense Reimbursement Fee Waiver or Reimbursement Total Annual Fund Operating Expenses After Expense Reimbursement Net Expenses (as a percentage of Assets) 1 Year Expense Example, with Redemption, 1 Year 3 Years Expense Example, with Redemption, 3 Years 5 Years Expense Example, with Redemption, 5 Years 10 Years Expense Example, with Redemption, 10 Years 2015 Annual Return 2015 2016 Annual Return 2016 2017 Annual Return 2017 2018 Annual Return 2018 2019 Annual Return 2019 2020 Annual Return 2020 2021 Annual Return 2021 2022 Annual Return 2022 2023 Annual Return 2023 2024 Annual Return 2024 One Year 1 Year Five Year 5 Years Since Inception of Fund Since Inception Inception Date of Fund Inception Date Risk/Return [Heading] Objective [Heading] Objective, Primary [Text Block] Objective, Secondary [Text Block] Expense [Heading] Expense Narrative [Text Block] Shareholder Fees Caption [Text] Shareholder Fees Column [Text] Maximum Cumulative Sales Charge (as a percentage of Offering Price) Maximum Cumulative Sales Charge (as a percentage) Maximum Sales Charge Imposed on Purchases (as a percentage of Offering Price) Maximum Deferred Sales Charge (as a percentage of Offering Price) Maximum Deferred Sales Charge (as a percentage) Maximum Sales Charge on Reinvested Dividends and Distributions (as a percentage) Redemption Fee (as a percentage of Amount Redeemed) Redemption Fee (as a percentage of Amount Redeemed) Redemption Fee Redemption Fee Exchange Fee (as a percentage of Amount Redeemed) Exchange Fee Maximum Account Fee (as a percentage of Assets) Maximum Account Fee Shareholder Fee, Other Operating Expenses Caption [Text] Operating Expenses Column [Text] Distribution or Similar (Non 12b-1) Fees Component1 Other Expenses Component2 Other Expenses Component3 Other Expenses Acquired Fund Fees and Expenses Acquired Fund Fees and Expenses Fee Waiver or Reimbursement over Assets, Date of Termination Portfolio Turnover [Heading] Portfolio Turnover [Text Block] Portfolio Turnover, Rate Expense Footnotes [Text Block] Expenses Deferred Charges [Text Block] Expenses Range of Exchange Fees [Text Block] Expense Breakpoint Discounts [Text] Expense Breakpoint, Minimum Investment Required [Amount] Expenses Represent Both Master and Feeder [Text] Expenses Explanation of Nonrecurring Account Fee [Text] Other Expenses, New Fund, Based on Estimates [Text] Acquired Fund Fees and Expenses, Based on Estimates [Text] Expenses Other Expenses Had Extraordinary Expenses Been Included [Text] Expenses Restated to Reflect Current [Text] Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text] Expense Example [Heading] Expense Example by Year [Heading] Expense Example Narrative [Text Block] Expense Example by, Year, Caption [Text] Expense Example, No Redemption Narrative [Text Block] Expense Example, No Redemption, By Year, Caption [Text] 1 Year Expense Example, No Redemption, 1 Year 3 Years Expense Example, No Redemption, 3 Years 5 Years Expense Example, No Redemption, 5 Years 10 Years Expense Example, No Redemption, 10 Years Expense Example Footnotes [Text Block] Expense Example Closing [Text Block] Strategy [Heading] Strategy Narrative [Text Block] Strategy Portfolio Concentration [Text] Risk [Heading] Risk [Text Block] Risk Footnotes [Text Block] Risk Closing [Text Block] Risk Caption Risk Column [Text] Bar Chart and Performance Table [Heading] Performance Narrative [Text Block] Performance Information Illustrates Variability of Returns [Text] Performance One Year or Less [Text] Performance Additional Market Index [Text] Performance Availability Phone [Text] Performance Availability Website Address [Text] Performance Past Does Not Indicate Future [Text] Bar Chart [Heading] Bar Chart Narrative [Text Block] Bar Chart Does Not Reflect Sales Loads [Text] Annual Return Caption [Text] Caption Annual Return, Column [Text] Column Annual Return, Inception Date Inception Date Annual Return 1990 Annual Return 1991 Annual Return 1992 Annual Return 1993 Annual Return 1994 Annual Return 1995 Annual Return 1996 Annual Return 1997 Annual Return 1998 Annual Return 1999 Annual Return 2000 Annual Return 2001 Annual Return 2002 Annual Return 2003 Annual Return 2004 Annual Return 2005 Annual Return 2006 Annual Return 2007 Annual Return 2008 Annual Return 2009 Annual Return 2010 Annual Return 2011 Annual Return 2012 Annual Return 2013 Annual Return 2014 Annual Return 2025 Bar Chart Footnotes [Text Block] Bar Chart Closing [Text Block] Bar Chart, Reason Selected Class Different from Immediately Preceding Period [Text] Bar Chart, Returns for Class Not Offered in Prospectus [Text] Year to Date Return, Label Bar Chart, Year to Date Return, Date Bar Chart, Year to Date Return Highest Quarterly Return, Label Label Highest Quarterly Return, Date Highest Quarterly Return Label Lowest Quarterly Return, Label Lowest Quarterly Return, Date Lowest Quarterly Return Performance Table Heading Performance Table Does Reflect Sales Loads Performance Table Market Index Changed Index No Deduction for Fees, Expenses, Taxes [Text] Performance Table Uses Highest Federal Rate Performance Table Not Relevant to Tax Deferred Performance Table One Class of after Tax Shown [Text] Performance Table Explanation after Tax Higher Performance Table Narrative Performance Table Footnotes, Reason Performance Information for Class Different from Immediately Preceding Period [Text] Performance Table Footnotes Performance Table Closing [Text Block] Average Annual Return, Caption Average Annual Return, Column Name Label 10 Years Ten Year Money Market Seven Day Yield, Caption [Text] Money Market Seven Day Yield Column [Text] Money Market Seven Day Yield Phone Money Market Seven Day Yield Money Market Seven Day Tax Equivalent Yield Thirty Day Yield Caption Thirty Day Yield Column [Text] Thirty Day Yield Phone Thirty Day Yield Thirty Day Tax Equivalent Yield Supplement to Prospectus [Text Block] S000065838 [Member] FlexShares Developed Markets ex-US Quality Low Volatility Index Fund FlexShares Developed Markets ex-US Quality Low Volatility Index Fund Member fst:MSCIWorldExUSIndexMember MSCI World Ex US Index [Member] MSCI World ex-US Index Northern Trust Developed Markets Ex US Quality Low Volatility Index Northern Trust Developed Markets Ex US Quality Low Volatility Index [Member] Northern Trust Developed Markets ex-US Quality Low Volatility Index℠ C000212720 [Member] FlexShares Developed Markets ex-US Quality Low Volatility Index Fund FlexShares Developed Markets ex-US Quality Low Volatility Index Fund Depositary Receipts Risk Depositary Receipts Risk [Member] Foreign Securities Risk Foreign Securities Risk [Member] Geographic Risk Geographic Risk [Member] S000065839 [Member] FlexShares Emerging Markets Quality Low Volatility Index Fund FlexShares Emerging Markets Quality Low Volatility Index Fund Member fst:MSCIEmergingMarketsIndexMember MSCI Emerging Markets Index [Member] MSCI Emerging Markets Index Northern Trust Emerging Markets Quality Low Volatility Index Northern Trust Emerging Markets Quality Low Volatility Index [Member] Northern Trust Emerging Markets Quality Low Volatility Index℠ C000212721 [Member] FlexShares Emerging Markets Quality Low Volatility Index Fund FlexShares Emerging Markets Quality Low Volatility Index Fund Emerging Markets Risk Emerging Markets Risk [Member] Valuation Risk Valuation Risk [Member] S000033312 [Member] FlexShares Morningstar US Market Factor Tilt Index Fund FlexShares Morningstar US Market Factor Tilt Index Fund Member Russell3000 Index Russell3000 Index [Member] Russell 3000 Index fst:MorningstarUSMarketFactorTiltIndexMember Morningstar US Market Factor Tilt Index [Member] Morningstar® US Market Factor Tilt Index℠ C000102368 [Member] FlexShares Morningstar US Market Factor Tilt Index Fund FlexShares Morningstar US Market Factor Tilt Index Fund Value Investing Risk Value Investing Risk [Member] Mid and Small Cap Stock Risk Mid and Small Cap Stock Risk [Member] S000033313 [Member] FlexShares Morningstar Developed Markets ex-US Factor Tilt Index Fund FlexShares Morningstar Developed Markets ex-US Factor Tilt Index Fund Member MSCI World Ex USA Index MSCI World Ex USA Index [Member] MSCI World ex-USA Index Morningstar Developed Markets Ex US Factor Tilt Index Morningstar Developed Markets Ex US Factor Tilt Index [Member] Morningstar® Developed Markets ex-US Factor Tilt Index℠ C000102369 [Member] FlexShares Morningstar Developed Markets ex-US Factor Tilt Index Fund FlexShares Morningstar Developed Markets ex-US Factor Tilt Index Fund S000033314 [Member] FlexShares Morningstar Emerging Markets Factor Tilt Index Fund FlexShares Morningstar Emerging Markets Factor Tilt Index Fund Member Morningstar Emerging Markets Factor Tilt Index Morningstar Emerging Markets Factor Tilt Index [Member] Morningstar® Emerging Markets Factor Tilt Index℠ C000102370 [Member] FlexShares Morningstar Emerging Markets Factor Tilt Index Fund FlexShares Morningstar Emerging Markets Factor Tilt Index Fund S000050614 [Member] FlexShares US Quality Large Cap Index Fund FlexShares US Quality Large Cap Index Fund Member fst:SandP500IndexMember S And P 500 Index [Member] S&P 500 Index Northern Trust Quality Large Cap Index Northern Trust Quality Large Cap Index [Member] Northern Trust Quality Large Cap Index℠ C000159758 [Member] FlexShares US Quality Large Cap Index Fund FlexShares US Quality Large Cap Index Fund Momentum Risk Momentum Risk [Member] S000054498 [Member] FlexShares STOXX US ESG Select Index Fund FlexShares STOXX US ESG Select Index Fund Member STOXX USA ESG Select KPIs Index STOXX USA ESG Select KPIs Index [Member] STOXX® USA ESG Select KPIs Index℠ C000171075 [Member] FlexShares STOXX US ESG Select Index Fund FlexShares STOXX US ESG Select Index Fund ESG Investment Risk ESG Investment Risk [Member] S000054499 [Member] FlexShares STOXX Global ESG Select Index Fund FlexShares STOXX Global ESG Select Index Fund Member STOXX Global ESG Select KPIs Index STOXX Global ESG Select KPIs Index [Member] STOXX® Global ESG Select KPIs Index℠ fst:MSCIWorldIndexMember MSCI World Index [Member] MSCI World Index C000171076 [Member] FlexShares STOXX Global ESG Select Index Fund FlexShares STOXX Global ESG Select Index Fund S000073358 [Member] FlexShares ESG & Climate US Large Cap Core Index Fund FlexShares ESG & Climate US Large Cap Core Index Fund Member Northern Trust ESG Climate US Large Cap Core Index Northern Trust ESG Climate US Large Cap Core Index [Member] Northern Trust ESG & Climate US Large Cap Core Index℠ C000230177 [Member] FlexShares ESG & Climate US Large Cap Core Index Fund FlexShares ESG & Climate US Large Cap Core Index Fund New Fund Risk New Fund Risk [Member] S000073359 [Member] FlexShares ESG & Climate Developed Markets ex-US Core Index Fund FlexShares ESG & Climate Developed Markets ex-US Core Index Fund Member Northern Trust ESG And Climate Developed Markets Ex US Core Index Northern Trust ESG And Climate Developed Markets Ex US Core Index [Member] Northern Trust ESG & Climate Developed Markets ex-US Core Index℠ C000230178 [Member] FlexShares ESG & Climate Developed Markets ex-US Core Index Fund FlexShares ESG & Climate Developed Markets ex-US Core Index Fund S000033315 [Member] FlexShares Morningstar Global Upstream Natural Resources Index Fund FlexShares Morningstar Global Upstream Natural Resources Index Fund Member fst:MSCIACWIIndexMember MSCIACWIIndex [Member] MSCI ACWI Index Morningstar Global Upstream Natural Resources Index Morningstar Global Upstream Natural Resources Index [Member] Morningstar® Global Upstream Natural Resources Index℠ C000102371 [Member] FlexShares Morningstar Global Upstream Natural Resources Index Fund FlexShares Morningstar Global Upstream Natural Resources Index Fund S000042071 [Member] FlexShares STOXX Global Broad Infrastructure Index Fund FlexShares STOXX Global Broad Infrastructure Index Fund Member STOXX Global Broad Infrastructure Index STOXX Global Broad Infrastructure Index [Member] STOXX® Global Broad Infrastructure Index C000130666 [Member] FlexShares STOXX Global Broad Infrastructure Index Fund FlexShares STOXX Global Broad Infrastructure Index Fund MLP Tax Risk MLP Tax Risk [Member] REIT Risk REIT Risk [Member] MLP Risk MLP Risk [Member] Interest Rate Risks Interest Rate Risks [Member] S000043008 [Member] FlexShares Global Quality Real Estate Index Fund FlexShares Global Quality Real Estate Index Fund Member FTSE EPRA NAREIT Developed Index [Domain FTSE EPRA NAREIT Developed Index [Member] FTSE EPRA/NAREIT Developed Index℠ Northern Trust Global Quality Real Estate Index Northern Trust Global Quality Real Estate Index [Member] Northern Trust Global Quality Real Estate Index℠ C000133169 [Member] FlexShares Global Quality Real Estate Index Fund FlexShares Global Quality Real Estate Index Fund Real Estate Securities Risk Real Estate Securities Risk [Member] S000051556 [Member] FlexShares Real Assets Allocation Index Fund FlexShares Real Assets Allocation Index Fund Member fst:NorthernTrustRealAssetsAllocationIndexMember NorthernTrustRealAssetsAllocationIndex [Member] Northern Trust Real Assets Allocation Index℠ C000162239 [Member] FlexShares Real Assets Allocation Index Fund FlexShares Real Assets Allocation Index Fund Tax Risk Tax Risk [Member] Model Risk Model Risk [Member] Fund of Funds Risk Fund of Funds Risk [Member] S000038873 [Member] FlexShares Quality Dividend Index Fund FlexShares Quality Dividend Index Fund Member Northern Trust Quality Dividend Index Northern Trust Quality Dividend Index [Member] Northern Trust Quality Dividend Index℠ C000119637 [Member] FlexShares Quality Dividend Index Fund FlexShares Quality Dividend Index Fund Dividend Risk Dividend Risk [Member] Volatility Risk Volatility Risk [Member] S000038875 [Member] FlexShares Quality Dividend Defensive Index Fund FlexShares Quality Dividend Defensive Index Fund Member fst:NorthernTrustQualityDividendDefensiveIndexMember NorthernTrustQualityDividendDefensiveIndex [Member] Northern Trust Quality Dividend Defensive Index℠ C000119639 [Member] FlexShares Quality Dividend Defensive Index Fund FlexShares Quality Dividend Defensive Index Fund S000038876 [Member] FlexShares International Quality Dividend Index Fund FlexShares International Quality Dividend Index Fund Member fst:MSCIACWIexUSAIndexMember MSCIACWIexUSAIndex [Member] MSCI ACWI ex USA Index fst:NorthernTrustInternationalQualityDividendIndexMember NorthernTrustInternationalQualityDividendIndex [Member] Northern Trust International Quality Dividend Index℠ C000119640 [Member] FlexShares International Quality Dividend Index Fund FlexShares International Quality Dividend Index Fund S000038877 [Member] FlexShares International Quality Dividend Dynamic Index Fund FlexShares International Quality Dividend Dynamic Index Fund Member Northern Trust International Quality Dividend Dynamic Index Northern Trust International Quality Dividend Dynamic Index [Member] Northern Trust International Quality Dividend Dynamic Index℠ C000119641 [Member] FlexShares International Quality Dividend Dynamic Index Fund FlexShares International Quality Dividend Dynamic Index Fund S000033316 [Member] FlexShares iBoxx 3-Year Target Duration TIPS Index Fund FlexShares iBoxx 3-Year Target Duration TIPS Index Fund Member Bloomberg US Aggregate Bond Index Bloomberg US Aggregate Bond Index [Member] Bloomberg U.S. Aggregate Bond Index fst:IBoxxThreeYearTargetDurationTIPSIndexMember IBoxxThreeYearTargetDurationTIPSIndex [Member] iBoxx 3-Year Target Duration TIPS Index C000102372 [Member] FlexShares iBoxx 3-Year Target Duration TIPS Index Fund FlexShares iBoxx 3-Year Target Duration TIPS Index Fund Inflation Protected Security Risk Inflation Protected Security Risk [Member] Income Risk Income Risk [Member] Interest Rate Maturity Risk Interest Rate Maturity Risk [Member] TBA Transactions Risk TBA Transactions Risk [Member] Credit or Default Risk Credit or Default Risk [Member] Prepayment or Call Risk Prepayment or Call Risk [Member] S000034352 [Member] FlexShares iBoxx 5-Year Target Duration TIPS Index Fund FlexShares iBoxx 5-Year Target Duration TIPS Index Fund Member fst:IBoxx5YearTargetDurationTIPSIndexMember IBoxx5YearTargetDurationTIPSIndex [Member] iBoxx 5-Year Target Duration TIPS Index C000105758 [Member] FlexShares iBoxx 5-Year Target Duration TIPS Index Fund FlexShares iBoxx 5-Year Target Duration TIPS Index Fund S000046193 [Member] FlexShares Disciplined Duration MBS Index Fund FlexShares Disciplined Duration MBS Index Fund Member ICE BofA Constrained Duration US Mortgage Backed Securities Index ICE BofA Constrained Duration US Mortgage Backed Securities Index [Member] ICE BofA® Constrained Duration US Mortgage Backed Securities Index℠ C000144481 [Member] FlexShares Disciplined Duration MBS Index Fund FlexShares Disciplined Duration MBS Index Fund Mortgage Backed Pass Through Securities Risk Mortgage Backed Pass Through Securities Risk [Member] US Government Securities Risk US Government Securities Risk [Member] Cash Transactions Risk Cash Transactions Risk [Member] Debt Extension Risk Debt Extension Risk [Member] High Portfolio Turnover Risk High Portfolio Turnover Risk [Member] Liquidity Risk Liquidity Risk [Member] S000047257 [Member] FlexShares Credit-Scored US Corporate Bond Index Fund FlexShares Credit-Scored US Corporate Bond Index Fund Member Bloomberg US Intermediate Corporate Bond Index Bloomberg US Intermediate Corporate Bond Index [Member] Bloomberg U.S. Intermediate Corporate Bond Index Hybrid Northern Trust Credit Scored US Corporate Bond Index Hybrid Northern Trust Credit Scored US Corporate Bond Index [Member] Hybrid Northern Trust Credit-Scored US Corporate Bond Index℠/Northern Trust US Corporate Bond Quality Value Index℠ C000148066 [Member] FlexShares Credit-Scored US Corporate Bond Index Fund FlexShares Credit-Scored US Corporate Bond Index Fund Corporate Bond Risk Corporate Bond Risk [Member] Quality Value Score Risk Quality Value Score Risk [Member] Rule 144A Securities Risk Rule 144A Securities Risk [Member] S000050613 [Member] FlexShares Credit-Scored US Long Corporate Bond Index Fund FlexShares Credit-Scored US Long Corporate Bond Index Fund Member fst:BloombergLongUSCorporateBondIndexMember BloombergLongUSCorporateBondIndex [Member] Bloomberg Long U.S. Corporate Bond Index Hybrid Northern Trust Credit Scored US Long Corporate Bond Index Hybrid Northern Trust Credit Scored US Long Corporate Bond Index [Member] Hybrid Northern Trust Credit-Scored US Long Corporate Bond Index℠/Northern Trust US Long Corporate Bond Quality Value Index℠ C000159757 [Member] FlexShares Credit-Scored US Long Corporate Bond Index Fund FlexShares Credit-Scored US Long Corporate Bond Index Fund S000062125 [Member] FlexShares High Yield Value-Scored Bond Index Fund FlexShares High Yield Value-Scored Bond Index Fund Member Bloomberg Universal Index Bloomberg Universal Index [Member] Bloomberg Universal Index ICE BofA US High Yield Index ICE BofA US High Yield Index [Member] ICE BofA® US High Yield Index Northern Trust High Yield Value Scored US Corporate Bond Index Northern Trust High Yield Value Scored US Corporate Bond Index [Member] Northern Trust High Yield Value-Scored US Corporate Bond Index℠ C000201101 [Member] FlexShares High Yield Value-Scored Bond Index Fund FlexShares High Yield Value-Scored Bond Index Fund High Yield Securities Risk High Yield Securities Risk [Member] Distressed Securities Risk Distressed Securities Risk [Member] Substantial Volatility Risk Substantial Volatility Risk [Member] Value Score Risk Value Score Risk [Member] S000073362 [Member] FlexShares ESG & Climate Investment Grade Corporate Core Index Fund FlexShares ESG & Climate Investment Grade Corporate Core Index Fund Member fst:BloombergUSCorporateTotalReturnValueUnhedgedIndexMember BloombergUSCorporateTotalReturnValueUnhedgedIndex [Member] Bloomberg US Corporate Total Return Value Unhedged Index Northern Trust ESG Climate Investment Grade US Corporate Core Index Northern Trust ESG Climate Investment Grade US Corporate Core Index [Member] Northern Trust ESG & Climate Investment Grade US Corporate Core Index℠ C000230181 [Member] FlexShares ESG & Climate Investment Grade Corporate Core Index Fund FlexShares ESG & Climate Investment Grade Corporate Core Index Fund S000035596 [Member] FlexShares Ultra-Short Income Fund FlexShares Ultra-Short Income Fund Member Bloomberg Global Aggregate Bond Index Bloomberg Global Aggregate Bond Index [Member] Bloomberg Global Aggregate Bond Index fst:Bloomberg13MonthUsTreasuryBillIndexMember Bloomberg13MonthUsTreasuryBillIndex [Member] Bloomberg 1-3 Month U.S. Treasury Bill Index C000109007 [Member] FlexShares Ultra-Short Income Fund FlexShares Ultra-Short Income Fund Management Risk Management Risk [Member] Sector Risk Sector Risk [Member] Leveraging Risk Leveraging Risk [Member] Asset Backed and Mortgage Backed Securities Risk Asset Backed and Mortgage Backed Securities Risk [Member] Municipal Market Volatility Risk Municipal Market Volatility Risk [Member] S000055516 [Member] FlexShares Core Select Bond Fund FlexShares Core Select Bond Fund Member C000174705 [Member] FlexShares Core Select Bond Fund FlexShares Core Select Bond Fund Underlying Fund Risk Underlying Fund Risk [Member] Hedging Risk Hedging Risk [Member]